The over-all objective of the proposed project is to elucidate the etiological factors involved in bladder stone disease and to institute a program for the elimination of the condtion. The proposed work corresponds to Phase II of the project which will evaluate the effectiveness of oral orthophosphate supplementation in the elimination of the disease. The program will cover 1000 infants and pre-school children equally divided into two groups (orthophosphate supplement and placebo). Subjects in a given age range will be assigned randomly to each group. Field personnel, including doctors, nurses, nutritionists and village workers will be responsible for the proposed work. Their responsibilities include: a) administration of the supplement and placebo; b) recording signs and symptoms indicating the stone disease; c) recording morbidity data, especially diarrhea, fever and vomiting; d) performing microscopic examination of urine and other routine urinalysis; e) recording dietary intake with special emphasis on local vegetables and forest plants; and f) managing simple medical problems and referring to the health center when indicated. Biochemical determinations of the urine as well as the data analysis will be performed in Bangkok. Computer service is available for data processing. This phase would be the major effort for the project and would cover 4-1/2 years.